Study on non-classical effects of Knudsen layer in planar Couette flow using molecular dynamics simulations

Abstract

Accurate estimation of non-conserved quantities, such as viscous stress and heat flux, occupies an essential role when designing and inventing techniques for gas flows in rarefied and micro-scale conditions. The Knudsen layer is a locale where contemporary macroscopic models fail to capture the true physics, thereby providing inaccurate measures of the non-conserved quantities in the fluid flows. In the Knudsen layer region, where the gas-wall interaction leads to deviations from the classical Navier-Stokes-Fourier (NSF) formulations, higher-order accurate constitutive relations are required to ascertain the appropriate dynamics. Of particular importance are the velocity singularity and temperature jump near the walls. This work aims to study the mechanisms and flow dynamics in the Knudsen Layer from the atomistic perspective and examine the deviations occurring in the continuum theories. To this end, planar Couette flow for a monoatomic gas (Argon) is simulated using molecular dynamics simulations. The conserved and non-conserved variables are evaluated using the first principles of kinetic theory and compared with the results of DSMC solutions from the mesoscale analysis. The mechanisms, which lead to differences in velocity and temperature profiles with varying Knudsen and Mach numbers, are studied in detail. © 2024 Author(s).